On December 11, 2021, NASA’s Fermi Gamma-ray Space Telescope and Neil Gehrels Swift Observatory detected a burst of high-energy light emanating from the edge of a galaxy about 1 billion light-years away. The incident has challenged scientists’ perceptions of gamma-ray bursts (GRBs), the most powerful phenomena in the cosmos.

The burst GRB 211211A was the first long-lasting gamma-ray burst to be traced to the origin of a neutron star merger. Considered a paradigm shift, the outburst lasted about a minute and our follow-up observations led to the identification of a kilonova.

Eleonora Troja, an astrophysicist at the University of Rome who led another team studying the eruption, said: “Many years ago, Neil Gehrels, an astrophysicist and Swift’s namesake, suggested that neutron star mergers could produce some long bursts. The kilonova we observed is evidence that mergers are associated with these long-term events, forcing us to rethink how black holes form.”

Alessio Mei, a doctoral student at the Gran Sasso Science Institute in L’Aquila, Italy, who led a group studying the data, said: “This is the first time we’ve seen such an excess of high-energy gamma rays in the aftermath of a fusion event. Normally, that emission decreases over time. It is possible that these high-energy gamma rays come from collisions between visible light from the kilonova and electrons in particle jets. The jets may be weakened by the original explosion or new ones propelled by the resulting black hole or magnetar.”

Scientists believe that the heavy elements in the cosmos were produced by neutron star mergers. They based their calculations on the frequency of short bursts believed to occur in the cosmos. Now they also have to account for extended bursts in their calculations.

Regina Caputo, Swift project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said: “This result underscores the importance of our missions working together and with others to monitor these phenomena on multiple wavelengths. Similar coordinated efforts have hinted that some supernovae could produce short bursts, but this event is the final nail in the coffin for the simple dichotomy we’ve used for years. You never know when you might come across something surprising.”

Magazine references:

  1. Rastinejad, JC, Gompertz, BP, Levan, AJ et al. A kilonova after a prolonged gamma ray burst of 350 Mpc. Nature 612, 223-227 (2022). DOI: 10.1038/s41586-022-05390-w
  2. Troja, E., Fryer, CL, O’Connor, B., et al. A nearby long gamma-ray burst from a compact object merger. Nature 612, 228-231 (2022). DOI: 10.1038/s41586-022-05327-3
  3. Mei, A., Banerjee, B., Oganesyan, G. et al. Gigaelectronvolt emission from a compact binary fusion. Nature 612, 236-239 (2022). DOI: 10.1038/s41586-022-05404-7
  4. Gompertz, BP, Ravasio, ME, Nicholl, M. et al. The case for a minute-long fusion-driven gamma-ray burst of rapidly cooling synchrotron emission. Wet Astron (2022). DOI: 10.1038/s41550-022-01819-4